Parabola Foci Properties
The segments between the point of intersection of two tangents to a conic and their points of contact are seen from a focus under equal angles. the ratio of the distances of any point on a conic from a focus and the corresponding directrix is constant.
Encyclopaedia Britannica (New York: The Encyclopaedia Britannica Company, 1910) 11:703
Courtesy the private collection of Roy Winkelman